The proliferation and availability of computer systems together with networking capabilities provided by facilities such as the Internet, have provided means for the wide and almost effortless distribution of data. Once in electronic form, information may be readily copied and transmitted to almost endless numbers of recipients. This information may include digitized images or video. Because of the ease of making numerous copies of a digitized work, it is often difficult to enforce a copyright in the underlying work or to determine if the underlying work is subject to a copyright.
Several techniques have been proposed to address copyright protection of digital images. Those techniques that attempt to incorporate copyright information into the image data are generally known as “watermarking” in which copyright information is intermingled with the image data. One technique for incorporating such information into the image data uses steganography. Much has been written on the subject of steganography and is readily available on the worldwide web at the following URL's: http://www.jjtc.com/steganography/; http://www.stegoarchive.com/; http://www.cl.cam.ac.uk/˜fapp2/publications/index.html; and elsewhere. Patents directed to watermarking are further informative including Rhoads U.S. Patent Publication No. US 2001/0016051 A1 entitled “Method and Apparatus for Discerning Image Distortion by Reference to Encoded Marker Signals,” published Aug. 23, 2001; Leighton, U.S. Pat. No. 5,664,018, entitled “Watermarking Process Resilient to Collusion Attacks,” issued Sep. 2, 1997; Maes et al., U.S. Pat. No. 6,198,832, entitled “Embedding And Detecting a Watermark in Images,” issued Mar. 6, 2001; and Wong, U.S. Patent Publication No. US 2001/0046307 A1, entitled “Method and Apparatus for Digital Watermarking of Images,” published Nov. 29, 2001, all of which are incorporated herein by reference in their entireties.
In general, these watermarking techniques provide an invisible digital watermark by inserting watermark information into some portion of the image data, typically the Least Significant Bits (LSBs) of the image data so as to minimize distortion of the original image. In this case, the LSBs of intensity values for predetermined pixels are used to encode copyright information instead of intensity values. To retrieve the copyright information, a recipient must know and be able to identify the pixels containing the copyright information so as to extract information from the LSBs of the designated pixels. Thus, one weakness of such a watermarking scheme is its vulnerability to both accidental and deliberate attacks. This is because, in general, such techniques are sensitive to distortion of the image data caused by such operations as cropping and/or affine distortions, such as rotation and scaling of the image. Such distortions of the image make recovery of the watermark difficult or practically impossible.
In addition to use as a watermark, steganographic techniques are used to encode other information with an image, such as creation date, author, caption etc., and for the covert transmission of information. However, as with watermarks, this information may be rendered unretrievable by relatively minor distortion of the image.
Accordingly, there is a need in the art to provide a robust watermark and/or stegenaographic data encoding technique that are resistant to unintentional and deliberate attacks.